We have been led to a perception of the enzymes of detoxication as a coherent group of about thirty or so catalytic activities with specific features in common. These enzymes generally have a broad spectrum of substrates with specificity for a functional group rather than for the carbon skeleton. The substrates are usually lipophilic and normally feature a relatively low catalytic efficiency. Emphasis in this laboratory has been on enzymes active in conjugation reactions such as those catalyzed by glutathione transferases, aryl sulfotransferases, hydroxysteriod sulfo- transferases, and aryl N-methyltransferases. Work with the sulfotransferases is allowing characterization of seven hemogeneous enzymes from rat liver, active in the formation of sulfate esters of phenols, primary and secondary alcohols including hydroxysteroids, and organic hydroxylamines; peptides with an N-terminal tyrosine such as the enkephalins and cholecystakinin heptapeptide, are sulfate acceptors.